Can Windows XP x64 read, write, and boot from GPT disks?
Windows XP x64 Edition can use GPT disks for data only.
What you can do is make multiple partitions. Then install Windows on one of the partitions.
Though Why XP 64 bit? Drop that old POS, if you need to use some outdated program Emulate it a free Virtual machine software like Virtual Box.
What is the largest hard drive windows xp pro 64bit can handle ?
As said by Kurz, you shouldn't be using windows XP now, but also, Windows XP 64-bit isn't an official Microsoft OS, so you aren't using an official version of windows. I would recommend install Windows 7, windows 8, or windows 8.1 and then update to 10 if you are not gaming, stay at 7 8 or 8.1 if you are gaming.
I just want to know what the largest hard drive xp pro 64 bit will handle, the 2 tb is for 32 bit, I have no desire to upgrade, Iam perfectly happy with what I have.